Crews at Tampa Fire Station 6 were getting calls from people living nearby at about 9 a.m.complaining about irritated eyes and throats.

Near the port, that'susually a bad sign.

When they got to the Port a couple of blocks away, they figured out what the source of the problem was and warned thousands of people to stay indoors for close to an hour.

A plume of smoke and gas was rising from a sulfur storage tank at Gulf Sulphur.

Officials say workers there were battling a small fire that started during routine maintenance. They tried to douse the flames with steam, but thatonly created a new problem, because the roof of the tank had holes in it and the steam and gas were not contained.

"When you add water to sulfur in that state, it turns into sulfur dioxide which is -- if it gets out -- can cause some eye irritation and maybe some throat irritation," said Capt. Lonnie Benniefield.

Videoprovided byTampa Fire Rescue closer to the scene, shows Haz-Mat workers trying to contain the escaping gas cloud, but they soon realized the wind was pushing the fumes toward the city.

Sulfur dioxide, they say, can irritate the eyes, throat and skin, but it can also be even more dangerous for those with respiratory problems.

They issued a bulletin to Harbour Island, Channelside, evenin the southern part of Downtown Tampa, affecting thousands of people.

"For their safety we want to make sure that they stay inside so they don't expose themselves to any of the smoke that's going on right now," said Benniefield.

By midday, the gas cloud was dissipating. Residents and downtown workers were given the "all clear."

But it was all pretty alarming, they say.

Charmaine Castillo says she got the warning in an email from her office building managers explaining the danger.

"The building management sent around an email saying that there was a gas leak in the area," she said.

Amos Castillo was nervous about it. The first email wasn't filled with detail and he wondered what had gone wrong.

"The first thing I thought maybe it was a terrorist incident or maybe a ship or something hadcrashed," he said.